This application is for support for continuing research on the functional roles of P and M retinal ganglion cells in macaque monkeys, and of their targets in the lateral geniculate nucleus, the Parvocellular and Magnocellular neurons, respectively. One way to investigate function is to determine the photoreceptor inputs to receptive field centers and surrounds of the P and M ganglion cells, and relate the properties of the cells to known behavioral changes or in variances with different receptors. I will determine the cone inputs to the different ganglion cells by means of color exchange and field adaptation spectral sensitivity. Receptive field mechanisms will be isolated by using appropriate spatial stimuli. Then the function of the P and M pathways will be explored in the primary visual cortex, using similar methods of color exchange and field adaptation. Responses of P and M and Parvocellular and Magnocellular neurons are different enough that their characteristic color exchange functions may be traced in cortical pathways. A third experimental project will be the measurement of the contrast sensitivity of cortical cells in macaque V1 at different mean luminance levels, because previous work in my laboratory has implied that below 1 troland of retinal illumination the P and parvocellular cells are unresponsive, in the near periphery of the visual field. The retinal eccentricity dependence of this low-luminance unresponsiveness will also be explored at the retinal, geniculate and cortical levels of the visual pathway. In a separate project, the interactions between cortical neurons will be explored with multi-sinusoidal temporal modulation in order to look at nonlinear components or interactions. This project will involve comparison between cat area 17 neurons and macaque striate cells. Finally, we will measure the position-dependence of the response of macaque and cat cortical cells to contrast modulation, as another way of investigating cortical spatial nonlinear interactions. The use of chromatic as well as luminance contrast will allow us to relate this interaction to the P and M inputs to striate cortex. All of this work is motivated by a desire to study the normal cellular basis for color and pattern vision. It also has great relevance to retinal or neurological diseases which may affect the M or P cells selectively. Thus, this project has relevance to medical diagnosis and treatment of visual diseases in humans.